The aim is to characterize the water sorption of the glassy, load-bearing, polymers used in dentistry. Plan sheet specimens will be prepared by polymerization of methacrylates and dimethacrylates. Polymerization will be effected by most of the initiating systems used for dental materials, including photochemical techniques. In selected cases, residual monomer will be removed by gamma-irradiation and annealing. Dry specimens will be immersed in water and then periodically removed, mopped dry, and weighed until constant weight is approached. Subsequently, similar measurements will be made during drying. Data will be analyzed to provide equilibrium sorption values and diffusion coefficients, the latter by application of Fick's laws for the case of plane sheet geometry. In another test, measurements of linear changes in dimensions, on equilibrium water sorption, will be made microscopically and used to calculate volumetric changes in cases of isotropic expansion. Volumetric changes will also be determined more directly be periodically weighing specimens suspended in water, as in Archimedes' method. Volumetric data will be analyzed to deduce what fraction of the water uptake is not accompanied by swelling. The working hypothesis is that this is the fraction of water accommodated in microvoids. The general scientific discipline involved in the proposed work is diffusion in glassy polymers. This is a field which, recently, has been designated as requiring further work. The particular problem of water sorption of glassy polymers is an unavoidable responsibility for the field of dental materials. The health-relatedness of such work is that excessive water sorption is an important factor in restricting to temporary use chairside hard denture base reliners and crown and bridge resins. It is also a factor in the wear of composite tooth restorative materials and in the choice of polymers for denture bases. The long term objective is to relate water sorption of glassy polymers to chemical (crosslinks) and physical (microvoids) structure and thereby to design useful dental prostheses.